suddenly,

I have positional problems that manifest as breathing problems (sleep apnea). If I sleep flat on my back with my head only slightly tilted to the right, I go great. If my head falls/tilts to either side much more, I stop breathing and have stressful dreams. If I try to sleep on my side, I need to ball my pillow up so my neck stays straight. If not, stressful to nightmare dreams. My wife can predict how my morning will be by watching me sleep/breath.

Do you have access to a doctor who understands sleep apnea? Mine is central sleep apnea (CSA) meaning it is caused by the central nervous system. Obstructive (snoring) sleep apnea OSA) is far more common. Many doctors will dismiss you if they see no signs of OSA. Brain stem issues can cause CSA.

I suggest having someone observe you sleeping. If they see or hear you stop breathing, you will have a valid complaint for a sleep specialist. CSA is difficult to treat. I resolve mine by disciplined sleep position. There are breathing pacemakers that can cause the diaphragm to pull a breath. They are an expensive and drastic solution.